L21 Enzymes - Enzymes 1 Last Time Measuring the energy that can perform work in the cell Free energy G Free energy and metabolism exergonic and

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Unformatted text preview: Enzymes 1 Last Time Measuring the energy that can perform work in the cell - Free energy - G Free energy and metabolism - exergonic and endergonic reactions Coupling exergonic reactions with endergonic reactions to do work 2 Enzymes Enzymes are proteins speed up exergonic chemical reactions Enzyme activity is affected by the cellular environment pH and temperature Regulation of enzyme activity Allosteric inhibition and activation Feedback 3 glycosidic bond disaccharide (Sucrose) Breaking the glycosidic bond to separate two monomers = hydrolysis This is an EXERGONIC reaction This is an example of a CATABOLIC reaction 4 Sucrase = enzyme Exergonic ....however, will not happen quickly. Enzymes speed up exergonic reactions Fig. 8.13 http://www.lifeplusvitamins.com/images/captain-enzyme-3.jpg 5 Activation energy Activation energy (EA) - pushes reaction over energy barrier, so "downhill" part of reaction can occur Fig. 8.14 6 Enzymes lower activation energy barrier 7 Enzymes force reactants into unstable forms Reactants - move towards lower energy state (high free energy to low free energy) Allowing reaction to proceed. 8 Important points Exergonic reactions are spontaneous, -G Rate can be slow because of the energy barrier - reactants require a small amount of energy to clear the energy barrier Enzymes DO NOT affect the G of the reaction - Enzymes lower the activation energy (EA) required for the reaction to occur quickly. Enzymes affect RATE of reaction 9 How do enzymes work? (reactant) 10 ("induced fit" between enzyme and substrate) the handshake 11 12 Enzyme mechanisms for lowering EA 1. allows substrates to assemble in proper orientation 2. enzyme can stretch the bonds towards `transition state' conformation 3. provides appropriate microenvironment for reaction to occur 4. brief covalent interaction between side chain of amino acid and substrate 13 UREASE The first enzyme crystallized for study in 1926 urea + 2 H2O -----> ammonia + 2 CO2 Enzymes only act on a specific substrate http://www.bch.msu.edu/faculty/hausinger/urease.jpg 14 Enzymes are proteins! Denaturation properly folded protein denatured protein Renaturation 15 Temperature Environmental factors affect enzyme activity pH 16 Enzyme `helpers' Co - factors inorganic metals, like Cu, Mg, Zn, Fe Co - enzymes organic molecules, like Vitamins 17 Summary Enzymes are proteins that lower the EA of exergonic chemical reactions Enzymes, like all proteins, can be denatured depending on the environment Enzymes have optimal pH and temperatures for maximum function Sometimes associate with co-factors, which assist in the catalysis 18 Regulation of enzyme activity Inhibition competitive inhibition noncompetitive inhibition Activation Feedback 19 Competitive inhibitors Normal binding Competitive binding 20 Noncompetitive inhibitors Normal binding Non competitive inhibitor binding 21 Inhibitors Competitive - mimics - resemble normal substrate - bind active site - often reversible Noncompetitive - bind another part of enzyme (not active site) - enzyme changes shape as a result - loses activity 22 Toxins and poisons sarin -amanitin 23 `death cap' (Amanita phalloides) -amanitin - toxin found in some mushrooms inhibits enzyme that uses DNA template to synthesize RNA http://collectivesource.com/fungi/newpages/Amanita_phalloides.html 24 Bushnell, David A. et al. (2002) Proc. Natl. Acad. Sci. USA 99, 1218-1222 Copyright 2002 by the National Academy of Sciences 25 25 Sarin Sarin binds an enzyme that breaks down a neurotransmitter result is CONSTANT SIGNALING 26 Regulation of metabolism allosteric regulation can inhibit enzyme activity can activate enzyme activity Allo = "shape" Steric = "space" protein's function at one site is affected by a protein binding at another site 27 Allosteric activator Fig. 8.20 28 Allosteric inhibitor 29 Cooperativity 30 Feedback inhibition product of a pathway inhibits the activity of an early enzyme in the pathway = REGULATION 31 Summary Enzymes are proteins speed up exergonic chemical reactions Enzyme activity is affected by the cellular environment pH and temperature Regulation of enzyme activity Allosteric inhibition and activation Feedback 32 Next Time Respiration: electron transfer http://www.cbs.dtu.dk/staff/dave/roanoke/mitochondriadrawing.gif 33 ...
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This note was uploaded on 04/10/2008 for the course BIO 311C taught by Professor Satasivian during the Fall '08 term at University of Texas at Austin.

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